This invention relates to a process for the stereospecific polymerization of .alpha.-olefins and a catalytic system therefor.
Methods of supporting the titanium compound of Zieagler-Natta catalysts on a carrier to improve the catalyst activity have been developed in a commercial scale for polymerization of .alpha.-olefins and generally, have being employed for a catalyst for polymerization of ethylene.
However, in case of polymerization of .alpha.-olefins such as propylene and butene, a useful crystalline polymer can not be obtained unless the polymeric chain has an isotactic structure in which alkyl groups such as methyl or ethyl are stereospecifically regulated. Accordingly, catalysts improved only in polymerization activity as the case of ethylene polymerization cannot be considered to be a useful catalyst for polymerization of .alpha.-olefins and thus, regulating the stereospecificity of polymer is a significant matter.
In connection with this, there are provided methods adding an electron donative compound as a third component to a mixture of a carrier-type titanium compound supported on magnesium halide and an organoaluminum compound thereby improving the stereospecificity of polymers obtained (e.g. British Pat. No. 1,435,768). Also, Japanese Application Kokai No. 50-126950 discloses a catalytic system comprising a carrier-type titanium compound obtained by treating a copulverized product of magnesium halide and an organic acid ester with titanium tetrachloride and an organoaluminum compound. Furthermore, U.S. Pat. No. 4,220,745 discloses the stereospecific polymerization of .alpha.-olefins in the presence of a catalytic system comprising an activated titanium compound obtained by treating a copulverized product of magnesium halide and an aromatic orthocarboxylic acid ester with titanium tetrachloride, an organoaluminum compound and an electron donative compound. These catalysts are, however, still insufficient in the polymerization activity and the crystallinity of polymers obtained.